1. Field of the Invention
The present invention relates to systems and methods for controlling delivery of a pressurized flow of breathable gas to a patient and, more particularly, to a ventilation mask such as nasal mask, nasal prongs mask or nasal pillows mask for use in critical care ventilation, respiratory insufficiency or OSA (obstructive sleep apnea) with CPAP (Continuous Positive Airway Pressure) therapy and incorporating a heat and moisture exchange device which is uniquely configured to maximize the transmission of heat and moisture to and from air flowing through the ventilation mask.
2. Description of the Related Art
The use of ventilator and breathing circuits to provide respiratory assistance to a patient is well known in the medical arts. The ventilator and breathing circuit provides mechanical assistance to patients who are having difficulty breathing on their own. In certain types of breathing circuits, a ventilator unit or flow generator is fluidly connected to a ventilation mask worn by the patient. Such fluid connection is typically achieved through the use of ventilation tubing or a tubing circuit which is operative to deliver the ventilation gas from the flow generator to the patient via the mask worn by the patient.
In normal, unassisted respiration, heat and moisture are absorbed from the exhaled air by the inner walls of the oral and nasal cavities of the patient as the air travels from the patient's lungs to the outside environment. This heat and moisture is then transferred to the inhaled air in the next breath, helping to keep the mucus membranes of the patient's lungs humidified and at the proper temperature. Mechanical ventilation bypasses this natural system, often resulting in dry air of incorrect temperature being introduced into the oral and nasal cavities, and hence the lungs of the patient. After a period of time, the respiratory tract of the ventilated patient becomes dried, often causing discomfort. Thus, one of the known disadvantages of conventional breathing circuits is that the air delivered to the patient's lungs is not at the appropriate humidity and/or temperature level.
In order to provide for proper humidity and temperature of the air in ventilator and breathing circuits, it is known to integrate a heat and moisture exchange (HME) device into the breathing circuit. Typically, HME devices are placed into the breathing circuit somewhere within the flow path of the warm, moist air which is exhaled by the patient. The exhaled air enters the HME device, where the moisture and heat are absorbed by those materials used to fabricate the same. These materials then impart the absorbed heat and moisture to the inhaled air in the next breath. The retention of warmth and high humidity helps to prevent the patient's lungs and mucus layers from drying out. Currently known HME devices generally consist of a housing that contains a layer of flexible, fibrous, gas-permeable media or material. As indicated above, this media has the capacity to retain moisture and heat from the air that is exhaled from the patient's lungs, and then transfer the captured moisture and heat to the inhaled air when the patient is inhaling with the assistance of the flow generator. The fibrous material or media in the HME device may be made of foam or paper or other suitable materials that are untreated or treated with hygroscopic material.
However, currently known HME devices possess certain deficiencies which detract from their overall utility. More particularly, the structural attributes of currently known HME devices does not make them particularly well suited for integration into ventilation masks such as nasal prongs or nasal pillows masks. In this regard, nasal pillows masks typically comprise a housing or cushion, the size of which is adapted to allow it to be positioned below the patient's nostrils and above the patient's mouth. The resultant relatively small size or profile of the cushion does not lend itself to the easy integration of conventional HME devices directly therein. Rather, such HME devices must typically be located within the tubing circuit proximate, but not directly within, the cushion. As will be recognized, the integration of the HME device within the cushion immediately adjacent the patient's nostrils would optimize the ability of such HME device to facilitate the desired heat and moisture exchange operation with air inhaled and exhaled by a patient wearing the corresponding nasal pillows mask. The present invention addresses this issue by providing a ventilation mask such as a nasal pillows mask wherein an HME device is directly integrated into the housing or cushion thereof (thus residing in extremely close proximity to the patient's nostrils), and is further uniquely configured to induce a flow pattern between it and the cushion which maximizes the transmission of heat and moisture to air which is inhaled by and exhaled from the patient through the nasal pillows mask. These, as well as other features and advantages of the present invention will be described in more detail below.